Saudi officials said a suicide bomber killed two border guards and their commanding officer in an attack near the Iraqi border.
The Interior Ministry said the attack early Monday in Arar began with the bomber and another "terrorist" shooting at a border patrol. The guards returned fire, killing one person before the bomber detonated his explosives. Two other attackers were killed.
One of those killed was Saudi General Oudah al-Belawi, the senior border guard in Northern Borders province, which covers most of Saudi Arabia's frontier with Iraq.
An investigation of the incident is underway.
There was no immediate claim of responsibility. Although, Mustafa Alani, an Iraqi security analyst with close ties to Saudi Arabia's interior ministry, said the use of a suicide bomber pointed to the Islamic State group.
If confirmed, "it is the first attack by Islamic State itself against Saudi Arabia and is a clear message after Saudi Arabia entered the international coalition against it," Alani told Reuters.
Islamic State group leader Abu Bakr al-Baghdadi had called on supporters last month to launch attacks inside Saudi Arabia in retaliation for the kingdom taking part in the U.S.-led coalition carrying out airstrikes against the Islamic State group in Syria.
Since late September, U.S. and Saudi forces, along with those from Jordan, Bahrain and the United Arab Emirates, have conducted more than 600 airstrikes targeting the militants who took over large areas in Syria and Iraq.
The ministry said through state media that the four attackers carried assault rifles, handguns and hand grenades.
The remote desert crossing is next to Iraq's Anbar province, which has seen heated battles between Iraqi forces and Islamic State militants.
Saudi Arabia's more than 800 kilometer (500 mile) border with Iraq, defended by earthen barriers and fences and monitored by camera and radar, has been attacked in the past by mortar bombs fired from a distance, but more targeted strikes are rare.
Early last month, Saudi Arabia arrested 135 people, accusing them of scheming to sabotage security in the kingdom, smuggling weapons into the country and helping raise money for terrorist groups.
Some material for this article came from Reuters, AP and AFP.